Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.
Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors).
Communication Channels: tactile ; chemical
Other Communication Modes: pheromones
Perception Channels: tactile ; chemical
Parascaris equorum is not in danger of extinction.
Adult females are able to produce nearly 170,000 eggs daily. They are able to produce up to 60,000,000 eggs annually. The eggs are laid in the small intestine of the host and eventually exit the body in the feces. The life cycle of Parascaris equorum starts in the small intestine when the adult worms meet and mate. The eggs than travel through the intestines and end up in the feces. Prenatal infection is not known to occur. The egg then develops from the morula stage to the first juvenile stage to the second juvenile stage. If ingested by a horse, the egg travels to the small intestine where it hatches. The juvenile than penetrates the intestinal wall. The forth stage juvenile then travel into the alveoli and migrates back into the esophagus. After two more molts, the adults travel back to the small intestine and restart the cycle.
Parascaris equorum affects the young horses most often. It can cause pneumonia, bronchial hemorrhage, colic, and intestinal disturbances. These symptoms can lead to sluggishness and morbidity. These roundworms may cause intestinal perforation or obstruction. The older horses commonly are immune to the infection.
Negative Impacts: causes or carries domestic animal disease
This parasite infects horses and other equids.
Ecosystem Impact: parasite
Species Used as Host:
Parascaris equorum's main source of food is the liquid contents within the intestinal lumen. They eat by sucking up the liquid while moving through the intestines. It is probable that Parascaris equorum occasionally sucks the blood from the intestinal wall.
Animal Foods: blood; body fluids
Primary Diet: carnivore (Eats body fluids)
Parascaris equorum are found worldwide, wherever horses and other equids are.
Biogeographic Regions: nearctic ; palearctic ; oriental ; ethiopian ; neotropical ; australian ; antarctica
Other Geographic Terms: cosmopolitan
When fully grown Parascaris equorum lives in the small intestines of the horse.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Other Habitat Features: urban ; suburban ; agricultural
Parascaris equorum require 14-17 days for migration of the larvae through the liver and the lungs and 79-110 days to become gametogenically functional.
Parascaris equorum is large, cylindrical, and has a cuticle with three layers made of collagen and other compounds that protect the worm from the acids in the digestive tracts of animals. The adult male ranges from 15-28 cm. The females are much larger and can grow up to 50 cm. Parascaris equorum has three very large lips. Each of these lips has a transverse groove or labial sinus on the lateral margins, which divide the lip into apical and basal regions. The eggs of Parascaris equorum are almost spherical and have a brownish color. The eggs contain a 1-celled zygote and are between 90-100 microns in size.
Nematodes have longitudinal muscles along the body wall. The muscles are obliquely arranged in bands. Dorsal, ventral and longitudinal nerve cords are connected to the main body of the muscle.
Range length: 15 to 50 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently
These parasites are probably not preyed on directly. Larval mortality is high as most of the parasites do not reach appropriate hosts.
The life cycle of Parascaris equorum starts in the small intestine when the adult worms meet and mate. Females may produce a phermomone to attract males. The male coils around a female with his curved area over the female genital pore. The gubernaculum, made of cuticle tissue, guides spicules which extend through the cloaca and anus. Males use spicules to hold the female during copulation. Nematode sperm are amoeboid-like and lack flagella. The eggs than travel through the intestines and end up in the feces. Adult females can produce nearly 170,000 eggs daily and up to 60,000,000 eggs annually.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous
Parental Investment: pre-fertilization (Provisioning)
Parascaris equorum is a species of ascarid that is the equine roundworm. Amongst horse owners, the parasites are colloquially called "Ascarids". This is a host-specific helminth intestinal parasite that can infect horses, donkeys, and zebras. Horses up to six months of age are the most susceptible to infection. After this time, infection rates begin to decline and is extremely uncommon in horses over twelve months of age.[1] It cannot infect humans or other animals.[2] It is yellow-white in color, and females can become as large as 15 inches (38 cm) in length.[3] Found worldwide, P. equorum is one of the most difficult equine parasites to kill, requiring larger doses of more powerful anthelmintic medications than are needed for other equine parasites.[2]
P. equorum is sexually dimorphic, the females are significantly larger than males. While males only grow up to 15–28 cm in length, the females can grow up to 50 cm in length. They are a white colored, cylindrical worm and have three very large lips.[4] Mating occurs in the small intestine of the equid. The female is able to lay over 170,000 eggs in a day, and 60,000,000 eggs in a year.[5] Eggs have a thick, multilayered shell for protection and the ability to adhere to any surface they touch once expelled.[2] Eggs are expelled in feces, which are then consumed by a horse while eating contaminated grass or drinking contaminated water. In a three-month life cycle, the swallowed eggs become larva and migrate from the small intestines into blood vessels and from there travel to the liver, where they molt into another larval stage. From there, they migrate to the lungs, where they emerge from blood vessels into the alveoli.[2] They spend between 14 and 17 days migrating through the liver and lungs.[5] At this point, they are coughed up and re-swallowed, where the larvae mature into adult roundworms that produce eggs.[3] The worms take from 79 to 110 days to reach adulthood. P. equorum lives by sucking up the liquid contents of the intestine and may occasionally also suck blood from the intestinal wall.[5]
Horses may develop a cough and a nasal discharge during the lung migration stage. Scarring of internal organs, particularly the lungs and liver, can occur during parasite migration. Severe infestations of adult P. equorum can also cause colic, intestinal blockage and potential intestinal rupture. Feed absorption is often reduced, and other clinical signs may include unthriftiness, potbelly, rough hair coat, and slow growth.[3]
Severe infestations of P. equorum are able to create a mechanical blockage in the intestines. In some cases, deworming treatment may actually trigger an intestinal blockage of dead and dying parasites; for this reason, severe cases may require multiple treatments of milder drugs.[2]
Diagnosis of infestation can be found by looking for eggs in feces via a microscopic examination. The limitation of this method is that only mature worms can be detected via their eggs; immature larval forms are difficult to detect, and blood tests are unreliable.[2]
Mature horses appear to develop a certain degree of resistance to this parasite, but it is a concern for younger horses up to about two years old.[3] P. equorum is one of the few parasites where a natural immunity develops in the host.[2] However, when an infection is found in an adult horse, both the worm and egg counts are substantially low.[1]
Deworming can begin with foals at four to eight weeks of age and is repeated about every 60 days. Treatment is with anthelmintic medication, and rotating between different classes of anthelmintics is recommended.[6] Effective treatments include the macrocyclic lactones, notably ivermectin or moxidectin, which can kill the early larval stages before they migrate into the liver and lungs. Another class of effective medication are the benzimidazoles, such as fenbendazole. Pyrantel pamoate is also used, and a closely related variant, pyrantel tartrate, can be fed as a daily dose that is effective at killing larvae. Prior to development of these drugs, during the 1950s and 1960s, treatment with piperazine, dichlorvos and trichlorfon was used.[2]
Keeping pastures and stables free of manure has been shown to be effective in reducing parasite infestations in horses. Rotation of pastures, particularly by putting animals of other species into the rotation, can also reduce the amount of parasite infestation.[6]
Parascaris equorum is a species of ascarid that is the equine roundworm. Amongst horse owners, the parasites are colloquially called "Ascarids". This is a host-specific helminth intestinal parasite that can infect horses, donkeys, and zebras. Horses up to six months of age are the most susceptible to infection. After this time, infection rates begin to decline and is extremely uncommon in horses over twelve months of age. It cannot infect humans or other animals. It is yellow-white in color, and females can become as large as 15 inches (38 cm) in length. Found worldwide, P. equorum is one of the most difficult equine parasites to kill, requiring larger doses of more powerful anthelmintic medications than are needed for other equine parasites.
